We will design and evaluate a novel detector module for PET, and demonstrate that it would significantly increase the sensitivity and resolution, while making PET compact, light weight, and portable. The basic detector element proposed is based on the use of a novel light-detector called Solid State Photo- multiplier (SSPM) and LYSO scintillation crystals. Hamamatsu has developed a special ceramic-mounted SSPM for our company. Its compact size (2.4x1.9x0.85 mm) enables construction of PET scanners with a resolution close to a millimeter. Its thinness (0.85 mm) allows multiple layer of the detectors to be put in radial direction enabling the depth of interaction and inter-crystal scatter events. The specific aims of the Phase I of this project are to study, both through simulation as well as experiments with a variety of detector arrangements, the degree of improvements in: 1)- Spatial resolution, 2)- Sensitivity, 3)- Inter-crystal scatter correction, 4)- Depth of interaction identification, 5)- Scatter events rejection 6)- Singles rejection by improved time resolution. The experiments and simulations planned for the Phase I are directed to enable us to build the optimum detector configurations for the Phase II. Significance: Accurate intra-operative tumor localization is critical in a variety of clinical conditions. The ability to adapt PET to the operating room would allow for the generation of real time functional images of tumors , allowing for better tumor localization. The same detector module can be the basis of other larger configurations of portable PET, greatly expanding the application of PET in a variety of settings. [unreadable] [unreadable] [unreadable]